miR-34a carried by adipocyte exosomes inhibits the polarization of M1 macrophages in mouse osteolysis model.

OBJECTIVE

After bone prosthesis replacement, M1-type macrophage polarization can be induced by titanium (Ti) particles and produce inflammatory, leading to osteolysis. Adipocyte-derived exosomes (ADEs) exert immune-modulatory impact on the macrophage, while whether it can inhibit the macrophage polarization induced by Ti is unclear. This study focuses on the M1-type macrophage and aims to determine the effect of ADEs on Ti-induced M1-type macrophage polarization in osteolytic mice and the involved mechanism.

METHODS

Ti particle-induced osteolysis mouse model was established and macrophages were isolated from the osteolysis site. The levels of NLRP3 and specific markers for M1-type macrophage were determined. ADEs isolated from adipocyte cell line 3T3-L1, or conditioned ADEs with low-expressed miR-34a isolated from 3T3-L1 transfected with miR-34a inhibitor were co-cultured with RAW 264.7 to determine their impact on the polarization of macrophage.

RESULTS

ADEs reduced the M1-type macrophage polarization and caused the upregulation of miR-34a in macrophage of the osteolysis site of the osteolysis mouse model. Also, the level of miR-34a in ADEs was higher than that in the adipocyte. The conditioned ADEs expressed a low level of miR-34a and boosted the Ti-induced M1-type polarization. MiR-34a could target NLRP3 and negatively regulated its expression. Moreover, NLRP3 knockdown in macrophage restricted the conditioned ADEs to promote macrophage towards to Ti-induced M1-type polarization. The inhibitory function of ADEs on M1-type macrophage polarization was abolished by miR-34a silencing in the mouse osteolysis model.

CONCLUSION

The miR-34a carried by ADEs reduced the polarization of M1-type macrophages by targeting macrophage NLRP3 during Ti particle-induced osteolysis.